Two years ago, U.S. Rep. John B. Larson stunned many in Connecticut with an idea to build a system of highway tunnels under Hartford and East Hartford longer than Boston's "Big Dig."

Reactions to his plan ran from "brilliant and necessary" to "the mother of all pipe dreams," but Larson plowed ahead and asked state Department of Transportation officials to study the tunnel idea.

They did. In an analysis released in September, DOT traffic engineers said, in effect, that they don't think it will work.

Undeterred, Larson convened two forums on tunnels in the past two months, one featuring business and civic leaders from Seattle, which is replacing an aging highway viaduct with a tunnel, and another with a national tunneling expert.

So, does Connecticut cue Big Bertha and start drilling, or not?

Now that Democrats have taken control of the U.S. House of Representatives, Larson envisions a path forward. He said in a recent interview that he expects his party to bring out an infrastructure bill in the Spring, the first in eight years. As a member of the Ways and Means committee, Larson believes he is well positioned to bring some of the infrastructure spending to Connecticut.

But is a tunnel system with a price tag in the billions the best way to spend it?

Larson said he is trying to solve problems created by the placement, age and design of the 1960s-era highways: traffic congestion, neighborhood isolation, impeded connection to the Connecticut River and economic development, and decaying dikes along the river. He said in a recent statement that he thinks "tunneling is the best option for the Hartford Region" and would continue to advocate for it "until a better solution is presented."

State planners, however, think they have a better solution — to bring the I-84/I-91 interchange out of downtown to the North Meadows, allowing through traffic on I-84 to go around downtown and over a new bridge before reconnecting to the existing highway in East Hartford.

Aging viaducts

The tunnel story starts with efforts to replace the 2.5 mile series of viaducts that carry I-84 through much of Hartford. About 80 percent of the 1960s-era roadway was built on bridge stanchions that are now past their projected 50-year lifespan.

Early in the last decade the DOT considered repairing the viaduct in place. But a citizens group, the Hub of Hartford, formed and urged a different solution, one that would undo some of the damage the highway had done to the city.

The city, regional planners and eventually the DOT got behind the idea. Maintenance repairs were done — and continue — on the viaducts, but in 2012 the department also initiated a widely praised public planning process.

After looking at several options, the planners determined in 2017 that a highway at or slightly below grade was the best way to replace the viaduct system. It would, for example, allow city streets to cross over the roadway, diminishing the walling effect of the elevated highway.

This plan is moving ahead. The original highway was built on bridges in part to accommodate the railroad. The first step in bringing the highway to ground is to relocate some of the tracks and build a new station. Planning has started, and construction is a decade or more away.

But replacing the highway doesn't by itself improve worsening congestion. I-84 was built to carry 55,000 cars a day through Hartford; it now carries 175,000. In addition, I-84 shrinks from three lanes to two in both directions around the Bulkeley Bridge, constricting rush-hour traffic.

Another 100,000 vehicles traverse I-91 each day. The I-84/I-91 interchange, with 275,000 cars a day, is the worst bottleneck in the state, the second worst in New England and the 24th worst in the country, according to the American Transportation Research Institute.

Well aware of the problem, DOT Commissioner James Redeker in 2016 initiated a study of the I-84/I-91 interchange. The study began by focusing on three long-term options to reduce congestion: widening the historic stone-arch Bulkeley Bridge, moving the I-91/I-84 interchange north of downtown and building a new bridge over the Connecticut River, and running a highway across the southern tier of the city to connect with the Charter Oak Bridge.

At this point, in the winter of 2016-2017, seemingly out of left field, came the congressman with his tunnel concept.

Big plan

Larson, who was easily re-elected to an 11th term last week, pays close attention to infrastructure issues. He has been trying for years to get federal funds to repair the flood control system along the Connecticut River. All applaud this effort; the 1940s system of dikes, pumping stations and conduits is in an "unacceptable" state of repair, according to a 2013 inspection by the U.S. Army Corps of Engineers. Should the levees fail, Hartford could suffer a Katrina-like catastrophe.

Meeting with some engineers in the spring of 2016 about the dikes, Larson began to wonder if the dike and traffic congestion issues could be solved in one fell swoop, with a tunnel system. More meetings produced the tunnel proposal.

It is no small plan.

Larson's idea, which he always called a "preliminary concept," would include an east-west tunnel running four miles from Flatbush Avenue in Hartford under the southern tier of the city near Trinity College and Colt Park, and then under the river to the Roberts Street area in East Hartford. The north-south tunnel would run two miles from the North to the South Meadows. They would meet at a large cloverleaf intersection under Colt Park, which would add four-to-six miles of tunnels.

Larson's idea is that the tunnels would take the through traffic, allowing the existing roads and bridges to become boulevards for local traffic.

Larson asked the DOT people to examine the proposal.

The DOT's I-84 project team analyzed six potential solutions to the I-84/I-91 interchange, based on congestion abatement, mobility, safety and economic development. The results were made public at a Sept. 6 meeting of the I-84 Project Public Advisory Committee. The tunnel got a low score.

The main problem with the tunnels is that they won't carry local traffic, and most of the peak highway traffic — more than two thirds, according to the DOT — "wants local access to Hartford/East Hartford."

So tens of thousands of cars would still have to use the boulevards. If these are boulevards controlled by traffic signals, as many are, the congestion could be worse than it is today. In Seattle, two-thirds of peak load is through traffic, which means the city is able to put many of its local commuters on transit. Hartford has new north-south bus and rail transit options but virtually no east-west transit beyond local buses.

DOT planners also raised the issue of safety, such as getting emergency vehicles into the tunnels. Larson said the safety issues have been successfully addressed in tunnels across the country.

The solution the DOT planners most prefer is the so-called "northern alignment," which would move the I-84/I-91 interchange to the city's North Meadows. There would be a new connector from I-84 along the railroad right-of way through the Clay Hill neighborhood to the Meadows — a mecca of car dealerships — then over a new bridge and onto a state-owned right-of-way in East Hartford that would connect it back to I-84.

In essence, through traffic would circumvent downtown while local traffic would be accommodated downtown. The roadway would be capped where it traverses residential neighborhoods. Neighborhood opposition might be an issue, though preliminary feedback indicated many residents liked the idea of better access to the highway.

Redeker said the northern alignment would free up 150 acres of land in Hartford and 50 acres in East Hartford for development. The tunnel would presumably do the same.

Finally, there is the issue of cost. DOT officials estimate that the full tunnel system could cost as much as $50 billion. Larson said that figure is "ridiculous," and when he announced the concept he estimated the cost at $10 – $12 billion. At this point these are guesses; the project has not been penciled out.

The reason for the wide discrepancy in cost estimates is apparently because Larson's original proposal envisioned one tunnel in each corridor, probably with two tiers. The DOT planners think traffic volumes would require two adjacent tunnels in each main corridor, one in each direction, plus the interchange, or up to 18 miles of tunnels. The interchange tunnels would each have one lane, and the I-84 and I-91 mainline tunnels would have two tiers with two lanes on each tier, thus up to 54 lane miles.

Using Seattle's cost of $0.47 billion per lane mile, this translates to$25.38 billion in 2015 dollars for the Hartford project. Add a 3.5 percent cost escalation factor each year for 15 years and the cost rises to about $50 billion. Larson said he would not propose something that expensive.

Seattle's tunnel of just under two miles cost $3.2 billion (and will be paid for in part with tolls).

Larson said any solution will be expensive; the DOT agrees but says the tunnel will be far and away the most expensive.

So how is this (highly preliminary) dilemma resolved?

Points of agreement exist

Larson and the DOT agree that the original highway project, which separated the North End and Asylum Hill from downtown, cut the city off from the river, constricted downtown development and wasted potentially valuable land for a massive interchanges in Hartford and East Hartford, was a disastrous mistake.

They also agree that it is vitally important, as Larson said, to "get it right this time.

There is also a shared belief that the dikes on both sides of the river must be repaired. Larson is making progress on this; he announced on Oct. 23 that funding for an U.S. Army Corps of Engineers study of the levees, a "crucial first step" in getting federal funding for the repair project, had been approved as part of the recently passed America's Water Infrastructure Act of 2018. If the money is forthcoming, the dike repair could be split off as a separate project and done before the highway reconstruction.

Most observers like the idea of lowering I-91 through the city — whether in a drilled tunnel, a "cut and cover" tunnel, or other means — to fully reconnect the city to the river. Both the tunnel and "northern alignment" plans would lower I-91.

So the main point of disagreement centers on I-84 — namely, whether to run the through traffic in a tunnel and turn the road into a boulevard, or make it a lowered highway with a connector around downtown for through traffic.

Larson spokeswoman Mary Yatrousis said the Congressman hopes to "continue the conversation," talk to more experts, get better numbers, and reach a consensus.

The DOT commissioner agrees.

"It's not a this-year thing," Redeker said. "We can figure it out."

Meanwhile, he said, there are plenty of other important transportation infrastructure projects awaiting funding.